Our goal is to achieve a comprehensive understanding of the neural circuitry of the cat retina. This seems realistic now that fundamental neuron "types" have been defined in cat retina, and it is realized that there are only three to five dozen. Seventeen types are already synaptically linked and twelve are associated with a specific transmitter. Our approach is to reconstruct adjacent retinal neurons from electron micrographs of serial sections. In such a series certain neurons are labeled beforehand by the accumulation of a tritiated transmitter, by a monoclonal antibody coupled to HRP, or by a marker of activity, such as the reaction product of cytochrome oxidase. The strength of this approach is in the detail gathered on adjacent neurons for they can be "typed" by multiple criteria and then linked in synaptic circuits. Data can be gathered quantitatively, permitting the development and testing of specific hypotheses regarding function. For example, we have demonstrated within a single series multiple synaptic connections between eight types of neurons. Among these is a Beta/X-on cell with input from two types of cone biolar, one of which may be inhibitory. The receptive field center of the Beta/X-on cell, we hypothesize, may be generated by excitation from a depolarizing cone bipolar and simultaneous withdrawal of inhibition from a hyperpolarizing bipolar. We shall test the qualitative anatomical predictions of this "push-pull" hypothesis using the methods described above. We shall also develop an electrontic model of the Beta/X-on cell in order to test a quantitative version of the hypothesis. We anticipate that additional hypotheses to explain the physiology will develop naturally as we delineate new circuits. When retinal circuits are truly understood, it should be possible tgo mimic them with integrated semiconductor circuits. Such feature-detecting devices may have broad industrial applications and will be medically useful, most obviously for the blind.